Generally, a rotating metal cathode drum with a polished surface, and an insoluble metal anode which is disposed on more or less the lower half of this cathode drum and surrounds the circumference of the cathode drum, are used to manufacture electrolytic copper foils. A copper electrolytic solution is caused to flow between the above-mentioned drum and anode, and an electrical potential is applied across these parts, so that copper is electrodeposited on the cathode drum. Then, when the electrodeposited copper has reached a specified thickness, this deposited copper is peeled from the cathode drum, so that a copper foil is continuously manufactured.
The copper foil thus obtained is generally referred to as a raw foil; this foil is subsequently subject to several surface treatments, and is used in printed wiring boards or the like.
An outline of a conventional copper foil manufacturing apparatus is shown in FIG. 4. In this electrolytic copper foil manufacturing apparatus, a cathode drum 1 is disposed in an electrolytic bath at which accommodates an electrolytic solution. This cathode drum 1 rotates in a state in which the drum is partially immersed (i.e., more or less the lower half of the drum is immersed) in the electrolytic solution.
An insoluble anode 2 is disposed so that this anode surrounds the lower half of the circumference of the cathode drum 1. There is a fixed gap 3 between this cathode drum 1 and anode 2, and an electrolytic solution flows through this gap. Two anode plates are disposed in the apparatus shown in FIG. 4.
In this apparatus shown in FIG. 4, the electrolytic solution is supplied from below; the apparatus is constructed so that this electrolytic solution passes through the gap 3 between the cathode drum 1 and anode 2 and overflows from the upper rim of the anode 2, and so that this electrolytic solution is recirculated. A specified voltage can be maintained between the cathode drum 1 and anode 2 by interposing a rectifier between these members.
As the cathode drum 1 rotates, the thickness of the copper electrodeposited from the electrolytic solution increases, and when this thickness exceeds a certain thickness, the raw foil 4 is peeled away and continuously taken up. The thickness of the raw foil that is thus manufactured can be adjusted by adjusting the distance between the cathode drum 1 and the anode 2, the flow velocity of the electrolytic solution that is supplied, or the amount of electricity that is supplied.
In the copper foil that is manufactured by such an electrolytic copper foil manufacturing apparatus, the surface that contacts the cathode drum is a mirror surface; however, the surface on the opposite side is a rough surface with projections and indentations. In the case of ordinary electrolysis, the projections and indentations of this rough surface are severe, so that undercutting tends to occur during etching, and the achievement of a fine pattern is difficult.
Recently, meanwhile, as the density of printed wiring boards has increased, the narrowing of circuit width and the development of multi-layer circuits have led to a demand for copper foils that allow fine patterning. In order to achieve such fine patterning, a copper foil that is superior in terms of etching characteristics is required.
Furthermore, in regard to the performance values required in copper foils used in printed wiring boards, not only elongation at ordinary temperatures, but also high-temperature elongation characteristics for the purpose of preventing cracking caused by thermal stress, and a high tensile strength for dimensional stability of the printed wiring board, are required. However, copper foils of the above-mentioned type in which the projections and indentations of the rough surface are severe are completely unsuitable for fine patterning, as was described above. For such reasons, smoothing of the rough surface to a low profile has been investigated.
It is generally known that such a low profile can be achieved by adding large amounts of glue or thiourea to the electrolytic solution.
However, such additives lead to the problem of an abrupt drop in the elongation at ordinary temperatures and high temperatures, thus causing a great drop in the performance as a copper foil for use in printed wiring boards.